In many acoustic systems, such as traditional telephone systems and evolving voice-over-IP (VoIP) systems, it is desirable to minimize acoustic and electrical echoes. Typically, acoustic signals are first processed using echo cancellation techniques and then any residual echoes are processed using echo suppression techniques. For a detailed discussion of conventional echo control techniques, see, for example, M. M. Sondhi and D. A. Berkley entitled “Silencing Echoes On The Telephone Network,” Proceedings of the IEEE, Vol. 68, No. 8, pages 948-963, August 1980.
For example, a media processor in a voice-over-IP network typically includes an echo controller, such as a software-based echo canceler-suppressor. The echo controller eliminates acoustic and electrical echo originating, for example, from endpoints and line trunks that communicate via time-domain multiplex (TDM) connections. The echo controller is engaged in a variety of call topologies in which there is a TDM-to-IP speech-signal conversion boundary. For example, in a call from an IP terminal to a TDM terminal within the same port network, a media processor engages an echo controller to control acoustic echo originating at the TDM terminal that would otherwise be perceived by the IP phone user. When present, this acoustic echo is caused by the loudspeaker-to-microphone coupling in the TDM phone's handset, headset or speakerphone.
While existing echo suppression techniques provide adequate performance for most applications, they suffer from a number of limitations, which if overcome, could further improve the reduction of echoes in acoustic systems. A need therefore exists for improved echo suppression techniques for use in the echo suppressor component of an echo controller. Another need exists for an echo controller that demonstrates an improved ability to respond to acoustic echo originating from, for example, TDM speakerphones not equipped with an acoustic echo canceler. A further need exists for an echo controller that improves acoustic-echo control performance in essentially all call scenarios, such as speakerphones, handsets, and headsets, and improves electrical-echo control performance in call connections involving a TDM trunk.